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Disregarding hypoxia, what is the minimum air pressure that the human body can tolerate?

(i.e. at what air pressure would the blood start to boil, or skin start to burst, or whatever else might happen that would kill you but isn't related to oxygen?)

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    $\begingroup$ Can you separate lack of oxygen from low pressure? $\endgroup$
    – kmm
    Commented Apr 21, 2014 at 22:22
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    $\begingroup$ @kmm: I don't see why not. Just because there's not enough oxygen reaching the brain doesn't mean your blood would start boiling or your skin would start bursting... $\endgroup$
    – user541686
    Commented Apr 21, 2014 at 23:04
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    $\begingroup$ I think one cannot really separate the lack of oxygen from air pressure. Because the inside pressure balance the outside pressure, if the pressure is low outside, one cannot inhale lots of air without lung injury. Similarly, a scuba diver always inhale air at the pressure associated with its depth. (In consequence divers absorb much more oxygen (and consume more air) in deep water than in shallow water). You may eventually separate air pressure from oxygen if you consider someone who put a single arm or leg in a artificially very low pressure environment. $\endgroup$
    – Remi.b
    Commented Apr 23, 2014 at 9:00
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    $\begingroup$ @Remi.b: I don't see what's so hard about separating the two. Let me reword the question for you. Let's pretend the human body did not need oxygen/respiration at all, i.e. whatever you breathed in was exactly equal to whatever was breathed out (with no O2 or CO2 or anything else added or removed). What would be the minimum pressure it could survive in in that case? (If you're saying this has never been measured because, perhaps, it is impossible to measure, then please post that as an answer.) $\endgroup$
    – user541686
    Commented Apr 23, 2014 at 9:09
  • $\begingroup$ You might be interested to know what happen to our body in a vacuum. It does not tell you "the minimum pressure under which we can survive if we were to assume we don't need oxygen" but it might give you some sense of what you're looking for. $\endgroup$
    – Remi.b
    Commented Apr 23, 2014 at 9:23

3 Answers 3

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Disregarding hypoxia, the lowest atmospheric pressure the human body can withstand is around 6 percent sea level pressure, or 61.8 millibars, below that pressure the water and blood in your body starts to boil. Harry George Armstrong, a physician, and an airman, was the first to recognise this limit, which on Earth occurs at an altitude of roughly 63,000 feet, beyond which humans absolutely cannot survive in an unpressurised environment. The limit was named in his honour and so is called the Armstrong Limit. The lowest atmospheric pressure humans can breathe in, with a pure oxygen supply on hand, is roughly around 12.2 percent sea level air pressure or 121.7 millibars, the pressure found at 49,000 feet. Or, as a slightly madder alternative example, in a terraforming Mars situation, which might arise one day; a fit person could in theory walk around outside without a spacesuit on, but breathing from an oxygen tank, only when the atmospheric pressure got above about 120 millibars, and hope to survive for long.

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    $\begingroup$ For reference the natural atmospheric pressure on Mars is around 6 millibars. $\endgroup$
    – TylerH
    Commented Apr 22, 2021 at 15:56
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At sea level, where atmospheric pressure is 1 atm and oxygen is about 21% the partial pressure of oxygen is enough to saturate hemoglobin.

The lowest tolerable pressure of air is about 0.47 atm (475 millibars of atmospheric pressure) - recorded at 5950m altitude.

At about 0.35 atm (less than 356 millibars at around 8000m) life is impossible. Pulmonary and cerebral edema lead to death.

Source: Wikipedia, Effects of high altitude on humans

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  • $\begingroup$ You've got at least one number wrong. The "Death zone" at Mt Everest is considered to start at about 8000 meters, and the pressure there is about 0.75 atm. See engineeringtoolbox.com/air-altitude-pressure-d_462.html $\endgroup$
    – jarlemag
    Commented Apr 21, 2014 at 22:52
  • $\begingroup$ Just to clarify, I didn't mean that the "Death zone" altitude is the answer to the question, just that your altitude and pressure numbers don't match. Also, I couldn't find those numbers in the linked article. $\endgroup$
    – jarlemag
    Commented Apr 21, 2014 at 23:00
  • $\begingroup$ @jarlemag In the article Death zone pressure was in milibars. I converted it to atm. $\endgroup$
    – Cornelius
    Commented Apr 22, 2014 at 8:08
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    $\begingroup$ Sorry, my mistake. I mistook feet and meters in the table. There's still one mistake though: The lowest tolerable pressure (inhabited for two years) and 475 millibar figure is at the height of 5950 m. 5100 m is the height of the highest permanent settlement. $\endgroup$
    – jarlemag
    Commented Apr 22, 2014 at 12:57
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Humans can tolerate huge pressure changes with only a little oxygen in their lungs and blood system . IE: deep sea divers that dive down hundreds of feet into a huge pressure zone with out air tanks but just one big breath. Therefore, we should be able to live for a short while as well in the very low pressure area that is in the vacum of space. If placed in space suddenly, we would surely get the bends if we lived long enough. If still inside our damaged space craft the heated air would surely be sucked out, but the radiant heat of the mass of the whole area should still keep us warm enough for a short while. Outside the capsule in the direct radiation of the sun should not kill us suddenly either. Earth bond fire victims can tolerate over 70% damage and still live a short while. If forced outside into the shade of the damaged space craft, I believe it would be very cold but still very livable until we ran out of oxygen in our blood. Therefore I think we should have time left to think and do something physical to save ourselves from the very quick on set of asphyxiation before anything else takes it turn. IE: like do something like reach for the pressurized oxygen mask hanging on the wall like they have in airliners. If possible then we should freeze to death suffering from the bends.

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    $\begingroup$ Add some references to your claim. $\endgroup$
    – Dexter
    Commented Nov 4, 2015 at 5:53

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